1. Field of the Invention
The present invention relates generally to a charging method and apparatus, and more particularly, to a method and apparatus for performing wireless charging.
2. Description of the Related Art
A mobile terminal, such as a cell phone or a Personal Digital Assistant (PDA), is generally powered by a rechargeable battery that is recharged by electrical energy from a separate charging device. The charging device and the battery have their own separate external contact terminals, and are electrically connected by mechanically connecting the contact terminals to each other.
This contact-type charging scheme may often undergo contamination by foreign substances, such as moisture, causing incorrect battery charging, because the contact terminals protrude outward.
To address these and other problems, various wireless charging or non-contact charging technologies have recently been developed and used for many electronic devices.
The wireless charging technology, which uses wireless power transmission/reception, allows a user to automatically charge a rechargeable battery by simply placing it on a charging pad without connecting a separate charging connector to a mobile terminal with the rechargeable battery. Generally, devices that use the wireless charging technology include wireless electric toothbrushes and wireless electric shavers. This wireless charging technology may increase its waterproof features as it wirelessly charges electronic products, and may also increase mobility of electronic devices because it does not required wired chargers. Wireless charging technology is expected to evolve significantly in the growing era of electric vehicles.
This wireless charging technique includes an electromagnetic induction scheme using coils, a resonant scheme using resonance, and a Radio Frequency (RF)/microwave radiation scheme that converts electrical energy into a microwave and transfers the energy.
Up to now, the electromagnetic induction scheme has been primarily used. However, as many experiments of wirelessly transmitting power at a distance of several tens of meters using microwaves have recently been successful, it is highly expected that all electronic products may be wirelessly charged without cables in the near future.
The electromagnetic induction-based power transmission method is a scheme of transferring power between a primary coil and a secondary coil. Based on the principle that an induced current occurs when a magnet moves around coils, a time-varying magnetic field is generated in a transmitter and a current is induced at a receiver according to the change in the magnetic field, generating electrical energy. This phenomenon is called magnetic induction, and a magnetic induction-based power transmission method has excellent energy transmission efficiency.
The electromagnetic induction scheme has been applied to various devices. The non-contact charging technology, known as the conventional wireless charging technology, mostly includes electromagnetic induction methods, and this technology was originally applied to products such as electric shavers and electric toothbrushes that use nickel batteries.
As for the resonant scheme, Professor Soljacic at Massachusetts Institute of Technology (MIT) disclosed in 2005 a system that can be wirelessly supplied electricity, even though it is spaced several meters apart from a charging device, using the resonant scheme-based power transmission principle known as Coupled Mode Theory. The wireless charging system disclosed by the MIT team uses the physical concept that, based on the resonance theory, if a tuning fork resonates, an adjacent wine glass also resonates at the same oscillation frequency. The research team caused an electromagnetic wave containing electrical energy to resonate, instead of causing the tuning fork to resonate. It is known that unlike the electromagnetic wave, the resonant electrical energy does not affect surrounding machines and humans, because the resonant electrical energy is directly transferred only to the devices having the resonant frequency, and its unused portion is reabsorbed as an electromagnetic wave instead of spreading in the air.
The RF/microwave radiation scheme is a new-concept power transmission scheme that converts power energy into a microwave advantageous for its wireless transmission, and transfers it for energy supply. This scheme transfers electrical energy instead of transmitting signals used in wireless communication devices such as a radio receiver and a wireless phone. While the common communication system transmits signals on a carrier, the wireless power transmission system transmits only the carrier.
There is a need for the application of the foregoing wireless charging technology to the art of wireless communication devices, and to develop a method for causing power supply/demand devices to provide charging power to other devices when necessary.